The present invention relates to a work holding chuck for a machine tool such as a lathe, capstan lathe milling machine or the like. In particular, the present invention relates to a power operated chuck capable of clamping to hold a workpiece, or unclamping to release a workpiece, in a single, power driven stroke which can be controlled by displacement of a control member.
Conventional power chucks are either pneumatically or hydraulically operated and they rely for their power on power supplies separate from the driving motor of the machine tool; this represents a considerable disadvantage not only because of the expense of the chuck and its operating and control mechanism, but also because of the difficulty of mounting and setting up the chuck and its operating and control mechanism for proper operation.
The power source for known pneumatically operated chucks is normally an air compressor which operates to provide a supply of compressed air, via a control valve or a plurality of control valves, to energise at least one pneumatic actuator which acts, via a suitable linkage, on a draw bar or tube which passes through a hollow spindle of the machine. The draw bar or tube links the actuator to the operating mechanism of a chuck the jaws of which are caused to open or close by the action of the actuator on the draw bar or tube. Known hydraulic chucks operate in a similar manner. One of the disadvantages encountered with such known power operated chucks is that of transmitting the power to close or open the jaws when controlled to do so while nevertheless allowing the chuck to rotate with the jaws clamped, at perhaps a very high speed. In some known hydraulically operated chucks there are various mechanical parts linked to an hydraulic actuator mounted at the spindle end of the machine with a chuck being attached to the spindle via an hydraulic actuator. Even in this case, however, the source of hydraulic pressure must be separate from the machine.
Since the attachment, assembly and setting up of these known types of power chucks takes considerable time and labour they become effectively a part of the machine tool once fitted; although they are nominally interchangeable it has been found, in practice, that it is not worth doing so due to the amount of down time and labour involved.